A preparation of autologous peripheral blood mononuclear cells (PBMCs) radiolabeled with indium In 111 with radioisoptoic activity. Autologous PBMCs are isolated, expanded ex vivo, radiolabeled with indium In 111, and then infused back into the patient. Gamma scintigraphy may then be used to image gamma ray-emitting indium In 111 PBMCs localized in lymhoma tissue.